In the prior art, it has been suggested to use optically controlled semiconductor transistor switching devices, in order to afford electrical isolation between the control signal circuit and the controlled circuit. For example, in a paper by J. R. Biard et al., "Optoelectronics as Applied to Functional Electronic Blocks," Proceedings of the IEEE, Vol. 52, pp. 1529-1536 (1964), at p. 1533, several forms of optically actuated transistor (photo-transistor) switching devices were proposed for bidirectional control of electrical current flow. However, these proposals suffered from a limitation on the controlled voltage to 100 volts or less, owing to the problem of transistor breakdown caused by buildup of base-emitter voltage during the "off" condition of the switching devices. Moreover, the proposals in the prior art involving the back-to-back (series opposing) connection of a pair of photo-transistors between the terminals of the controlled circuit suffered from the requirement of fabricating a transistor with a breakdown voltage of greater than about 6 volts in combination with a sufficiently high inverse gain factor (inverse alpha) greater than about 0.99 in order to yield switchable (controlled) currents of reasonably high values, i.e., of about 100 milliamperes, thereby imposing a severe limitation upon the controlled voltage in the "off" condition. Accordingly, it would be desirable to have an optically controlled semiconductor switching device that avoids the shortcomings of the prior art, that is, a switch that can withstand at least about 200 volts in the "off" condition and can handle currents of 100 milliamps in the "on" condition.